1. Field of the Invention
The present invention relates generally to an optical information reading apparatus capable of reading optical information from an information medium such as bar code, wherein a laser beam is used for scanning the information medium.
2. Description of the Prior Art
There are conventionally known numerous laser bar code readers. Among them, Japanese Unexamined Patent Application 56-140467/81 discloses a typical laser bar code reader. In this prior art, a semiconductor laser is used as a laser source. A laser beam emitted from this semiconductor laser is collimated by a collimator lens. The laser beam, collimated by the collimator lens, is then reflected by a mirror. This mirror is driven by a stepping motor so as to cause a reciprocative sweep motion repeated at a low-frequency speed. A bar code is scanned by the laser beam reflected at the mirror. The laser beam, reflection at the bar code, returns to the mirror. The returning laser beam, after reflected at the mirror, is converged by a converging lens so as to focus on a photodetector. A signal received by the photodetector is thereafter used to decode the bar code. The optical reading operation of the bar code is accomplished in this manner.
Such a laser bar code reader is aimed at a bar code, with a laser beam having a predetermined scanning angle. However, if two, one being necessary to detect and the other being unnecessary, different bar codes happen to be in the scanning zone of the laser beam at the same time, the unnecessary bar code will be erroneously detected together with the bar code really wanted to detect. If this other bar code is not required to be scanned, a wrong decode data will be obtained. This kind of error tends to occur in cases where numerous bar codes are concentrated within a small area.
In order to avoid this problem, it will be necessary to place the laser bar code reader as close to the bar code to be scanned as possible. This will, however, spoil the inherent advantage of the non-contact type portable laser bar code reader.
Furthermore, although the semiconductor laser is advantageous in reducing size, weight, and power consumption of the laser bar code reader, some problems will take place due to disadvantageous properties of semiconductor laser. The semiconductor laser is so weak against static electricity and voltage surges that various characteristics such as light emitting mode, current-optical output characteristics, and spectrum characteristics are easily deteriorated and the life of the semiconductor laser is shortened undesirably.
Therefore, it is feared that the semiconductor laser may accidentally die within a warranty term. The laser bar code reader is usually operable without any trouble even if the life of the semiconductor laser is reduced to a certain degree. Therefore, it is quite difficult to predict the semiconductor laser will soon be fatally wasted. Furthermore, once the semiconductor laser is installed in the laser bar code reader, it is usually difficult to check how the semiconductor laser is deteriorated. Although the components of the laser bar code reader may be disassembled to check the semiconductor laser, disassembling the laser bar code reader is not practical or recommended.